The present invention relates to a fuze safety-and-arming devices, and more particularly to a fuze safety-and-arming device for spin-stabilized projectiles, the device having a plurality of novel, rotary movements to arm the fuze.
Safety and arming devices, which in themselves have no target detecting capability, are used in spin-stabilized projectile fuzes to keep the fuze in the safe condition until the projectile has been launched and has travelled a safe distance from the launcher, after which the devices arm and are ready to detonate the projectile whenever the fuze firing signal is generated. These devices generally comply with disign safety requirements by providing the required safety in the logistics life of a fuze from manufacture through launch. However, these type devices, which usually depend on an explosive train interrupter or rotor having its center of mass displaced from its rotational axis and this axis displaced from the axis of projectile spin to supply arming torque under a spin environment, have a common inherent weakness in being non-fail-safe. Failure modes can be induced which could cause the devices to arm soon after launch and well before safe separation. Under these circumstances a close-aboard premature detonation may occur, depending upon the type of firing mechanism used in the target detecting fuze.
These potential failure modes reside in the timing mechanism that provides safe separation Under certain conditions of undected discrepant manufacture or abnormally severe launch shocks, it is possible for the safe separation timer to fail in such manner as to cause it to disengage and allow the device to arm essentially instantaneously after gun exit. Some state-of-the-art safety-and-arming (S & A) devices incorporate pseudo fail-safe or premature-trap mechanisms which provide some protection against these failure modes. However, such mechanisms are not fully effective. In general, the state-of-the-art S & A devices do not completely satisfy the design goal of a truly fail-safe mechanism.
Consequently, a need exists for an S & A device with fail-safe characteristics inherent in the nature of its design concept. Such a concept would therefore be less vulnerable to discrepant manufacture and unforeseen environmental effects, and less dependent on auxiliary safety mechanisms with safety failure modes within themselves.
The present invention overcomes the above-discussed drawbacks by providing an odometer-type S & A mechanism which employs a balanced roter pivoted about its center of mass, the pivot being collinear with the projectile spin axis. The rotor thus becomes inertially passive in a constant spin environment. Centrifugal force exerts no driving torque on the rotor and will not drive it to the armed position if the rotor should disengage from the arming gear train. In such case, a fail-safe condition, or dud, results. This principle is totally different from the prior art odometer S & A mechanisms which utilize the rotation of an off-balanced rotor.